Zika virus, an illness transmitted to people through mosquito bites, has recently been linked to a congenital condition that causes newborns to have unusually small heads. Microcephaly, the name of the defect, causes smaller than normal cerebrums in babies and improperly developed brains.

Even still, the CDC has acknowledged that "additional studies are needed to further characterize this relationship." At this point, they're advising pregnant women to "consider postponing travel to the areas where Zika virus transmission is ongoing." All travelers to countries where evidence of the virus has been found are advised to take precautions to avoid mosquito bites such as wearing long sleeves and using bug repellent and mosquito nets.

According to the Hawaii State Department of Health, the Zika virus has been linked to one American case of the birth defect. Most cases of Zika have only been reported in travelers returning from abroad.